A helical pile is a segmented deep foundation system with helical load-bearing plates usually welded to a central steel shaft. The helical plates usually have a uniform pitch and are spaced far enough apart so that they function independently as individual bearing elements. Installation typically involves driving the shaft in rotation by means of a hydraulic motor. Shaft segments (with or without load-bearing plates) may be added until a desired soil depth or load-bearing capacity is reached.
The central steel shafts that carry the helical bearing plates are typically square or round (i.e., circular) in cross-section. Round and square shaft segments may be used in combination, for example, in areas where soft/loose soils are located above the bearing strata (i.e., hard/dense soils) for the bearing plates. The round shaft, which has a greater section modulus, will resist columnar buckling in the soft/loose soil. The square shaft will allow adequate penetration of the helices into the hard/dense material to achieve proper load-bearing capacity without “spin-out,” i.e., loss of thrust of the helices in the soft/loose material. Shaft segments typically are joined with complicated, costly fabricated transition couplings. Bolts, which fasten the shaft segments to the coupling, bear at least some of the axial compression load.